1. Technical Field
The present invention relates to a barrier film and a method of producing a barrier film.
2. Related Art
Silicon nitride films fabricated by parallel plate RF plasma CVD methods using silane gas, ammonia gas and nitrogen gas and the like as raw materials are used as passivation films for semiconductors. When a silicon nitride film is to be used as a barrier film for a low glass transition temperature (Tg) material such as a resin or an organic thin film, film formation must be conducted at high speed, and at a low substrate temperature of approximately 200° C. or lower. However, silicon nitride films formed under these types of conditions may oxidize under conditions of high temperature and high humidity, causing a deterioration in the barrier properties.
H. Kubota et al. have proposed a technique, in Journal of Luminescence, 2000, 87 to 89, page 56, in which a silicon nitride film is formed using only silane gas and nitrogen gas, without the use of ammonia gas. Furthermore, JP 05-6890 A, JP 05-335345 A, JP 06-291114 A and JP 2002-158226 A have proposed the lamination of a plurality of silicon nitride films with differing properties. Moreover, JP 2004-63304 A and JP 2005-222732 A have proposed applications of laminated structures containing a plurality of silicon nitride films with differing properties formed at a low substrate temperature to organic electroluminescent elements.
However, with the method disclosed by Kubota et al. in Journal of Luminescence, 2000, 87 to 89, page 56, the resulting silicon nitride film tends to suffer from large quantities of pinholes and the formation of dark spots, and the color of the silicon nitride film is brown, meaning use of the film in optical applications or as a barrier film is problematic. Forming this type of silicon nitride film with a thin enough film thickness (for example, 50 nm or less) to prevent any significant deterioration in the optical transmittance is one possible technique, but reducing the film thickness raises other problems such as a deterioration in the coating properties and an increase in the number of pinholes.
Furthermore, the methods disclosed in JP 05-6890 A, JP 05-335345 A and JP 2002-158226 A are all designed with the purpose of controlling the level of internal stress and the hydrogen content when film formation is conducted at a high substrate temperature of approximately 240 to 400° C., and make no reference to the conditions required for suppressing oxidation of the film at low substrate temperatures, simply because the film undergoes almost no oxidation under high substrate temperature conditions. JP 05-6890 A describes the internal compressive stress and the hydrogen content, but the level of stress and the hydrogen content are not essential factors in suppressing oxidation of the film at low substrate temperatures. JP 05-335345 A and JP 2002-158226 A describe the hydrogen content and the refractive index, but these are also not essential factors. JP 06-291114 A describes the ratio between the peak surface areas for N—H bonds and Si—H bonds within the infrared absorption spectrum for the film (namely, the ratio N—H/Si—H), but under the prescribed conditions of a ratio of 2 or less, oxidation of the film cannot be suppressed.
JP 2004-63304 A and JP 2005-222732 A have been designed with the purpose of controlling the stress within the film, and use only silane, nitrogen and hydrogen gases as the film formation gases, without the use of ammonia. Furthermore, although reference is made to Si—H bonds, the Si—H bonds are not an essential factor in improving the oxidation resistance, and oxidation of the film cannot be suppressed based solely on this factor.
The present invention provides a barrier film and a method of producing the barrier film that exhibit superior resistance to oxidation under conditions of high temperature and high humidity, suffer from minimal pinholes, and exhibit a high degree of optical transmittance.